Yes, plum seeds are edible. But your body can not digest a plum seed. It will give you some stomach pain or other stomach related problems. The taste of plum seed is also not good. I think it is better to avoid eating plum seed.

Plum seeds are edible but they do not have a very good taste to them. Just about every seed in fruit are edible but most are hard and have no flavor and just contain a bitter flavor. But nothing bad will happen if a plum seed is consumed besides a bland taste.

Sort of, you indeed can eat it. The problem would be it coming out the other end, your body cant digest a plum seed. They are also slightly toxic, not at a deadly level but it may give you a upset stomach. I would not think they would taste good either, large seeds are quite bitter.